1. Field of the Invention
The invention relates to devices for cleaning soot, ash and other sediment that tends to collect on heat transfer structures within heat exchangers. These cleaning devices include sootblowers in which a jet or blast of steam, air or another blowing medium is directed through a sootblower tube and out one or more nozzles onto the surfaces of the heat transfer structure to loosen and remove accumulated deposits of soot, ash and the like. These cleaning devices also include rappers in which a hammer-like head raps a header or other part of the heat transfer structure.
2. Description of the Prior Art
Prior soot cleaning devices pose a common problem, that of sealing around a movable sootblower tube or tube rapper shaft that extends through the wall of a boiler, superheater, preheater, or other heat exchanger. For example, Terry, U.S. Pat. No. 4,093,243, issued June 6, 1978, shows a rather elaborate ring-shaped seal, which is positioned around a retractable and rotatable sootblower tube as it extends through a wall box into a boiler chamber. Tuomaala, U.S. Pat. No. 3,835,817, issued, Sept. 17, 1974, shows a rotatable drive shaft for a rapper device that extends through a boiler wall, however, the problem of sealing that is presented by such a shaft is not discussed. Tomasicchio, U.S. Pat. No. 4,018,267, shows an oscillator type of soot cleaning device where a shaft from a pneumatic actuator passes through the wall of a heat exchanger and where an annular plug seal is used at the point of shaft penetration. While such seals might be acceptable for heat exchangers using clean gases at low or nearly atmospheric internal pressure, they present a problem where a heated, highly pressurized gas is present. This is the case presented by the boilers and superheaters used for heat transfer and heat recovery in coal gasification plants.
In such plants, typical mechanical seals would present three disadvantages. First, any leakage or failure would result in the escape of the heated, noxious or potentially combustible gas into the plant environment. Second, such seals would be formed at a pressure boundary between the high internal pressure of the heat exchanger and a much lower pressure outside the heat exchanger. Mechanical seals would be more likely to leak or fail under this pressure differential. And third, it would be difficult to design a simple and efficient mechanical seal for these heat exchangers that would accommodate the retraction, extension or rotation of a cleaning device through a wall of a heat exchanger vessel.